Impact-induced initiation of Snowball Earth: A model study

During the Neoproterozoic and Paleoproterozoic eras, geological evidence points to several “Snowball Earth” episodes when most of Earth’s surface was covered in ice. These global-scale glaciations represent the most marked climate changes in Earth’s history. We show that the impact winter following an asteroid impact comparable in size to the Chicxulub impact could have led to a runaway ice-albedo feedback and global glaciation. Using a state-of-the-art atmosphere-ocean climate model, we simulate the climate response following an impact for preindustrial, Last Glacial Maximum (LGM), Cretaceous-like, and Neoproterozoic climates. While warm ocean temperatures in the preindustrial and Cretaceous-like climates prevent Snowball initiation, the colder oceans of the LGM and cold Neoproterozoic climate scenarios rapidly form sea ice and demonstrate high sensitivity to the initial condition of the ocean. Given suggestions of a cold pre-Snowball climate, we argue the initiation of Snowball Earth by a large impact is a robust possible mechanism, as previously suggested by others, and conclude by discussing geologic tests.


Figure S1 :
Figure S1: Response of surface temperature and top-of-atmosphere (TOA) energy imbalance for the 4⇥CO 2 simulations in response to 6.6, 200, and 2000 Gt sulfate aerosol injection scenarios.(a) Global-mean surface temperature response.(b) Net TOA energy imbalance.

Figure S2 :
Figure S2: Snapshots of sea ice thickness following the 200 Gt radiative forcing scenario applied to the LGM climate.

Figure S3 :
Figure S3: Snapshots of sea ice thickness following the 200 Gt radiative forcing scenario applied to the 720 Ma (750 ppm) climate.

Figure S4 :
Figure S4: Snapshots of zonal-mean ocean temperatures as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the LGM climate.

Figure S5 :
Figure S5: Snapshots of zonal-mean ocean temperatures as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the preindustrial climate.

Figure S6 :
Figure S6: Snapshots of zonal-mean ocean temperatures as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the 720 Ma (750 ppm) climate.

Figure S7 :
Figure S7: Snapshots of zonal-mean ocean temperatures as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the 720 Ma (1500 ppm) climate.

Figure S8 :
Figure S8: Snapshots of zonal-mean ocean temperatures as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the 4⇥CO 2 climate.

Figure S9 :
Figure S9: Eulerian streamfunction for the global meridional overturning circulation, shown as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the LGM climate.

Figure S10 :
Figure S10: Eulerian streamfunction for the global meridional overturning circulation, shown as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the preindustrial climate.

Figure S11 :
Figure S11: Eulerian streamfunction for the global meridional overturning circulation, shown as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the 720 Ma (750 ppm) climate.

Figure S12 :
Figure S12: Eulerian streamfunction for the global meridional overturning circulation, shown as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the 720 Ma (1500 ppm) climate.

Figure S13 :
Figure S13: Eulerian streamfunction for the global meridional overturning circulation, shown as a function of latitude and depth, following the 200 Gt radiative forcing scenario applied to the 4⇥CO 2 climate.

Figure S14 :
Figure S14: Response of GMOC strength to the 6.6, 200, and 2000 Gt radiative forcing scenarios.(a) GMOC strength in the preindustrial simulations.(b) As in (a), but for the LGM simulations.(c) As in (a), but for the 4⇥CO 2 simulations.(d) As in (a), but for the 720 Ma (750 ppm) simulations.(e) As in (a), but for the 720 Ma (1500 ppm) simulations.GMOC strength is computed as the maximum of the annual-mean Eulerian streamfunction below 750m and to the north of 20°N.

Figure S15 :
Figure S15: Response of sea ice coverage and global mean ocean temperature to the 200 Gt sulfate aerosol radiative forcing scenario applied to the LGM climate.(a) Sea ice coverage in the LGM simulation, with and without an abrupt 1000 ppm CO 2 injection.(b) Ocean temperature response in the LGM simulation, with and without an abrupt 1000 ppm CO 2 injection.